1. Field of the Invention
The present invention in an aspect thereof relates to a travelling wave amplifier (TWA), in particular, relates to a TWA with suppressed jitter.
2. Related Background Art
One type of optical transmitter often implements with an optical signal source including, for instance, a semiconductor laser diode (LD), an optical modulator type of the electro-absorption (EA) modulator or the Mach-Zhender (MZ) modulator, and a driver to drive the optical modulator. An optical transmitter whose operation speed reaches 25 Gbps, 40 Gbps and so on, sometimes exceeds these speed, is necessary for rising and falling times of an optical output therefrom less than 10 picoseconds (ps). A driver to drive such an optical modulator is inevitably requested for a wide frequency band. An amplifier, or a driver with the configuration of, what is called, the travelling wave amplifier (TWA) is one of the best solutions for the wide band amplifier.
A TWA implemented with, what is called, hetero-bipolar transistor (HBT) has become popular in the field. Especially, an HBT with the cascade connection, namely, an HBT with another HBT connected in series to the former one has been used for a TWA application. However, the cascade connection sometimes brings a substantial jitter in an output thereof.